IN THE BORDERLANDS of southwestern Arizona lie the remains of Hunters Hole, a clump of tangled marshland sprawling across the lower Colorado River. This 440-acre wetland just south of Yuma was once so full of ducks people couldn't sleep for all the quacking, and an angler could snare a fish so fat it filled a frying pan. Cocopah Indians relied on the bounty of Hunters Hole in days when the only line separating the United States from Mexico was the river itself. As new settlers moved in, the area became a cross-cultural meeting place, where German farmers fished and hunted alongside tribal members.

"It was a way of life," says Cocopah elder Colin Soto, "not just for Cocopah, but for everybody."

That life faded over the last century as the once-full flows of the Colorado turned to little more than a trickle; invasive trees overran the shores, and communities changed. Rather than a place teeming with flotillas of birds and fish, Hunters Hole became a dense thicket of tamarisk, littered with the occasional old car, discarded shoes and bullet shells. It became a forgotten place, where bandits and illegal immigrants hid amid the brush. "That camaraderie, the social ties didn't really exist anymore," says Soto. "It all dwindled down to nothing without anyone really noticing."

Now, almost 30 groups, ranging from the Cocopah Indian Tribe to the U.S. Border Patrol, are teaming up to rescue this degraded habitat and rid it of crime. This effort entails the unlikely marriage of habitat restoration and national security. "I guess we all have the same goal in mind," says Arizona Border Patrol supervisory agent Carlos Dominguez. "Restore the area and make it safer."

That common ground has not always existed. The Border Patrol has been criticized for tearing up the desert as it pursues illegal immigrants. And while a proposed border fence could keep out border crossers who litter and trample sensitive ecosystems, it would also close important wildlife corridors.

Occasionally, the Border Patrol has helped with restoration, but mostly in a peripheral sense. Earlier this summer, Dominguez was one of several agents cleaning up trash along the California border, and recently, Arizona-based Border Patrol agents guarded workers as they cleared roughly 100 acres of non-native vegetation from the Cocopah Tribe's western reservation.

The Hunters Hole project significantly advances the Border Patrol's role in restoring borderland habitat. Planners see the project as a possible alternative to "the fence," as well as a way to foster more environmentally friendly patrolling efforts.

THE PROJECT IS COMING NONE TOO SOON. Crime has invaded the lower Colorado as though it were a derelict urban neighborhood. At least two people a year have been murdered there since 2004, and during the last year and a half alone, there were more than 250 armed robberies involving at least 1,500 victims, says Yuma County Sheriff Lieutenant David McBride, an eightfold increase from the previous year. Most of those victims, he says, are illegal immigrants.

But police officers have also fallen prey to area bandits: Since 2005, 20 have been injured, and there have been more than 50 assaults on officers. Twenty-foot-high walls of tangled branches mask people standing 10 feet away, says Dominguez, making bandits virtually invisible. "I wouldn't send my worst enemy down there to hunt or fish," agrees lead restoration planner Fred Phillips. "Hunters Hole is rampant with crime."

Violence and the lack of strong partnerships hindered previous restoration efforts. But now, the Border Patrol and the Yuma County sheriff have agreed to provide protection to researchers and other volunteers as they work in the field. "In order to restore Hunters Hole, we're going to have to secure it," says Dominguez.

THE EFFORT TO CLEAN UP Hunters Hole is modeled on the nearby Yuma East Wetlands project, a roughly 1,400-acre wetland adjacent to town. Though situated farther from the border than Hunters Hole, the Yuma East Wetlands exhibited similar problems - a degraded and trashed wetland, harboring vagrants and illegal activity.

The marsh is an important Quechan tribal area, and in late 2005, the tribe began working with Phillips and other collaborators, including the Yuma Crossing Natural Heritage Area, on restoration. In contrast to the sluggish pace of many environmental recovery efforts, sections of East Yuma were transformed in little more than a year, with native cattail marshes and flocks of migratory birds replacing tangles of salt cedar and trash. One can now visit areas like Ibis Lake Marsh to watch great egrets tip-toeing amongst the reeds.

Hunters Hole should be similar, except that along with restoring the wetland, crews will also incorporate patrol routes and levees into the landscape, melding security into the natural environment.

Restoration crews will excavate five miles of existing canal swamped by invasive vegetation and replant its banks with native cattail, bulrush and mesquite. Groundwater wells will re-supply water to the dried-out wetlands as well as to a 60-foot-wide channel running the length of Hunters Hole. And native vegetation will blanket the entire area, opening the view to illegal activity and providing habitat for wildlife, such as the endangered southwestern willow flycatcher and Yuma clapper rail.

Phillips estimates the project's cost to be about $7 million, funded primarily through grants. He has already received almost $200,000 from sources such as the Yuma Crossing Natural Heritage Area, the U.S. Bureau of Reclamation and the Walton Family Foundation. Restoration, says Phillips, should be under way by early 2008.

In the meantime, Cocopah elder Soto looks forward to a day when wildlife returns to Hunters Hole, and the river near his home is once again filled with fish. For him, restoration is a necessity, a treasure beyond all price: "We have a saying," he says. "If the river dies, we die."